Aristarchus of Samos

Aristarchus of Samos (; , ; ) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day. He also supported the theory of Anaxagoras that the Sun was just another star.

Born in Samos in approximately 310 BC, Aristarchus likely moved to Alexandria and became a student of Strato of Lampsacus, who later became the head of the Peripatetic school in Greece. According to Ptolemy, Aristarchus observed the summer solstice of 280 BC. Vitruvius writes that Aristarchus built two different sundials: one a flat disc; and one hemispherical. Aristarchus estimated the sizes of the Sun and Moon as compared to Earth, and the distances from the Earth to the Sun and to the Moon. His estimate that the Sun was 7 times larger than Earth (it's actually 109 times, in diameter) brought about the further insight that the Sun's greater size made it the most natural central point of the universe, as opposed to Earth.

Aristarchus was influenced by the concept presented by Philolaus of Croton (385 BC) of a fire at the center of the universe (i.e. by contemporary understanding, at the center of the Earth). Aristarchus recast this "central fire" as the Sun, and he arranged the other planets in their correct order of distance around the Sun.

Like Anaxagoras before him, Aristarchus suspected that the stars were just other bodies like the Sun, albeit farther away from Earth. His astronomical ideas were often rejected in favor of the geocentric theories of Aristotle and Ptolemy. Nicolaus Copernicus knew that Aristarchus had a 'moving Earth' theory, although it is unlikely that Copernicus was aware that it was a heliocentric theory. Provided by Wikipedia